Joe,

You're right...by default MM .NET assumes single-column foreign parent key fields. You can add support for multi-column foreign parent key fields by adding a ForeignParentKeyFields string array property to your business object, then overriding the methods that work with the foreign parent key field which are:

PopulateForeignParentKeyField(), (and if you're using mementos) MementoGet() and MementoSet().